Medical waste is sterilized and disposed. Conventionally, methods for applying steam and treating with an autoclave or treating with gases, such as formalin gas and ethylene oxide gas, or the like have been used as sterilization methods. However, there are fears of an incomplete sterilization when applying only live steam to medical waste and in addition, in many cases, a portion of the medical waste is decomposed or volatized by the application of steam, which may cause a bad odor and toxic components, so that such bad odor and toxic components become problems. Since a high-pressured container is used for an autoclave, the autoclave is so large-scale that its safety management is troublesome. Gas treatment is costly from the viewpoint of its apparatus and management in measures against leakage of gases because gases are harmful to body. Recent medical waste in various shapes may make it difficult to be dealt with after such sterilization treatment.